Optical fibers are used as remote delivery systems for high-powered laser energy and have become invaluable in a wide range of medical applications and in the treatment of a variety of diseases. When used in the treatment of blocked arteries, for example, many benefits are achieved, such as the acceleration of the healing process and the discouragement of scar tissue, by the cauterizing properties of the transported radiation. Laser energy conducted through a flexible waveguide, such as an optical fiber, has been used successfully for photocoagulation, hypothermic therapies, photoactivation of drugs and various other procedures.
Optical fibers are one of the most practical ways to deliver high powered radiation with very little loss of energy. The low attenuation is achieved by encasing the optical fiber in a polymer coating, or cladding. However, there are certain limitations to the use of optical fibers. Optical fibers are delicate—making them prone to breakage by excessive bending, shock or high temperatures. If the fiber breaks, radiation is released at the fault site which can quickly lead to melting or photodecomposition of the polymer coating surrounding the fiber as well as the instrument in which the fiber is encased. In addition, the fault can result in exposure of the patient and/or the clinicians to injurious high-energy radiation. When used in percutaneous operations, the energy transmitted through the fiber is often at a sufficient level that a break in the fiber can cause significant damage to blood vessels and surrounding tissue.
To prevent catastrophic device failures while delivering phototherapeutic energy during laser procedures, mechanisms for detecting failure are needed. It is desirable for the operator to determine and to be reasonably confident that the laser energy being directed to the treatment site is within certain predetermined desirable limits, that is, the energy is known to exceed a certain base or minimum therapeutic level, while not exceeding a certain upper limit. An indication that the laser beam energy is within a predetermined range enables the procedure to be more reliable, expedient, reproducible, and efficacious.
Moreover, it is highly desirable to have control systems that can detect problems in laser phototherapy before the problems become dangerous to the patient and/or destructive to the treatment apparatus. An automated monitoring system, and interlocked switch for shutting off the laser beam as the power fiber begins to fail, would satisfy a long felt need in the art. Currently available methods used to detect optical fiber faults have serious shortcomings including lack of sensitivity and inefficiency in detecting optical faults which allow considerable damage to occur (e.g., charring or combustion of polymeric tubing materials) before a signal is generated.
One known approach is to monitor radiation that propagates back through the treatment fiber (or a parallel transmission path) to detect changes in infrared radiation (“blackbody radiation”) that would indicate overheating of the instrument somewhere along the optical path. However, optical fiber cladding generates only small amounts of blackbody radiation until it undergoes chemical decomposition, and thus systems that rely on optical feedback can allow a significant amount of radiation to be released prior to signaling a shut-off protocol.
The present invention is directed to solving the technical problem of providing improved sensitivity in the detection of overheating, quick feedback, and continuous monitoring so that a better shut-off device for laser energy delivery systems is achievable.